The WikiLeaks founder, Julian Assange, will discover on Wednesday whether he is to be deported to Sweden to face allegations of rape and sexual assault when the supreme court delivers its verdict on his appeal.

The seven-strong panel of justices is expected to focus on the narrow issue of whether or not the European arrest warrant (EAW) requesting the 40-year-old Australian's extradition, which has been issued by the Swedish prosecutor, is valid.

EU treaty provisions governing extradition specify that a warrant must be drawn up by "competent judicial authorities". Lawyers for Assange argue that a prosecutor is not a judge or a "judicial" official. The court's judgment, expected to be relatively short, will include an explanation of the reasons for the decision.

Clare Montgomery QC, for the Swedish authorities, had argued that the arrest warrant was valid because judicial authorities, at least in the preliminary stages of investigations where arrest is being sought, need not be independent and impartial.

If the supreme court blocks the Swedish extradition request it could throw the EAW system into turmoil and have significant implications for other extradition cases within Europe.

The seven justices who heard the appeal are Lord Phillips, Lord Walker, Lady Hale, Lord Brown, Lord Mance, Lord Kerr and Lord Dyson. The fact that so many judges are considering the case suggests they recognise it is a particularly complex and significant issue. The two-day appeal hearing was held at the beginning of February.

Assange, who denies the allegations against him, can appeal to the European court of human rights if he loses the case. The ECHR must respond within 14 days to indicate whether or not it will accept the case.

If the court were to decline to take the case then he would be extradited to Sweden "as soon as arrangements can be made", according to the Crown Prosecution Service. If his case does go to Strasbourg then extradition is likely to be delayed and his current bail conditions continue until that legal process reached a conclusion. Assange is required to wear an electronic ankle tag and report to the police daily.